Disclosed herein are adhesive compositions containing cottonseed protein, and one or more of the following components: (i) soy protein, (ii) a polysaccharide, or (iii) at least one modifier selected from a carboxylic acid, a dicarboxylic acid, a phosphorus-containing acid or ester, a cationic amino acid, a quaternary ammonium salt, or mixtures thereof. Also disclosed are processes for producing an adhesive composition, involving mixing cottonseed protein and one or more of the following components: (i) soy protein, (ii) a polysaccharide, and (iii) at least one modifier selected from a carboxylic acid, a dicarboxylic acid, a phosphorus-containing acid or ester, a cationic amino acid, a quaternary ammonium salt, or mixtures thereof, and optionally (iv) water, plasticizer, or mixtures thereof. Furthermore, there are disclosed methods of bonding a first article to a second article, involving (a) producing an adhesive composition by mixing cottonseed protein, and at least one the following components: (i) soy protein, (ii) a polysaccharide, and (iii) at least one modifier selected from a carboxylic acid, a dicarboxylic acid, a cationic amino acid, a quaternary ammonium salt, or mixtures thereof, and optionally (iv) water, plasticizer, or mixtures thereof, at a pH of about 4 to about 12 and at a temperature of about 20° to about 60° C.; (b) depositing on a surface of the first article the adhesive composition thereby creating a binding area; and (c) contacting the binding area with a surface of the second article; and (d) applying heat and pressure to bond the first article to the second article.
The global wood adhesives and binders market is valued at $13.15 billion with a volume of 16,200 kilo tons in 2013 (Transparency Market Research, Wood adhesives and binders market—Global industry analysis, size, share, growth, trends and forecast, 2014-2020; 2014, http://www.transparencymarketresearch.com). Most wood adhesives currently in use are based on urea-formaldehyde, melamine-urea-formaldehyde, or phenol-formaldehyde resins. In order to decrease the usage of formaldehyde and petroleum-derived raw materials, there has been a partial shift in the past 15 years towards more eco-friendly bio-based wood adhesives, e.g., those based on soy and cellulose (Pizzi, A., J. Adhes. Sci. Technol., 20(8): 829-846 (2006); Kumar, R., et al., Ind. Crop Prod., 16: 155-172 (2002); Wang, D., et al., Trans ASABE, 52: 173-177 (2009); Frihart, C. R., and M. J. Birkeland, Am. Chem. Soc. Symp. Series, 1178: 167-192 (2014)). In particular, soy protein seems to be increasingly accepted in wood adhesive formulations (Sun, S., and K. Bian, J. Am. Oil Chem. Soc., 76: 977-980 (1999); Kalapathy, U., et al., J. Am. Oil Chem. Soc., 72: 507-510 (1995)) with several products having been commercialized (Li, K., et al., J. Am. Oil Chem. Soc., 81:487-491 (2004); Allen, A. J., et al., Forest Prod. J., 60(6): 534-540 (2010); Orr, L., Wood adhesives—A market opportunity study, Omni Tech International, Ltd., Midland, Mich., 2007, http://www.soynewuses.org/downloads/reports/final_WoodAdhesivesMarketOpportunity.pdf).
Cottonseed protein isolate can be prepared from defatted cottonseed meal by alkaline extraction followed by acidic precipitation (Berardi, L. C., et al., Food Tech., 23: 75-82 (1969); Martinez, W. H., et al., J. Agric. Food Chem., 18: 961-968 (1970)). In a previous work, we showed that cottonseed protein isolate exhibited superior adhesive strength and improved hot water resistance relative to soy protein isolate when used to bind maple wood veneer (Cheng, H. N., et al., Ind. Crops Prod., 46: 399-403 (2013)). In a follow-up study, sequential fractionation of cottonseed meal was studied and it was found that the adhesive properties of water and phosphate-buffer washed solid fractions were almost as good as cottonseed protein isolate (He, Z., et al., J. Am. Oil Chem. Soc., 91: 151-158 (2014)). These fractions were later tested on maple and poplar veneers with similar results (He, Z., et al., Int. J. Adhes. Adhes., 50: 102-106 (2014)).
Modification of protein formulations with alkali, guanidine hydrochloride, sodium dodecyl sulfonate, and urea has been shown to affect the adhesive properties of soy protein (Cheng, H. N., et al., 2013; Sun, S., and K. Bian, 1999; Hettiarachchy, N. S., et al., J. Am. Oil Chem. Soc., 72:1461-1464 (1995); Huang, W., and X. Sun, J. Am. Oil Chem. Soc., 77:101-104 (2000); Huang, W., and X. Sun, J. Am. Oil Chem. Soc., 77:705-708 (2000)) and cottonseed protein (Cheng, H. N., et al., 2013). Other modifiers previously studied with soy proteins included various plasticizers (Mo, X., and X. Sun, J. Am. Oil Chem. Soc., 79: 197-202 (2002)), ethylene glycol and its polymers (Chen, M., et al., BioResources, 10: 41-54 (2015)), cationic polyacrylamide (Xu, H., et al., BioResources, 9: 4667-4678 (2014)), clay (Zhang, Y., et al., BioResources, 8: 1283-1291 (2013)), calcium carbonate (Liu, D., et al., Bioresource Technol., 101: 6235-6241 (2010)), and combinations of acid, base, and salt (Lin, Q., et al., Int. J. Adhes. Adhes., 34: 11-16 (2012)).
In the present study, we developed adhesive compositions containing cottonseed protein and other components and surprisingly found that they exhibited improved adhesive strength.